Plastic microbeads (PMs) were recently placed in the spotlight after the discovery of tons of these tiny pieces of petrochemical polymers being accumulated in lakes, rivers and oceans. Scientific studies reported that 808 trillion microbeads are being washed down household drains every day in the US. Although these bits of polymer are used in a variety of applications, cosmetic products are by far the first source of PMs in the waste water streams. These microparticles are used as the abrasive ingredient in some toothpaste and as exfoliating agent in many shower gels, facial scrubs. The popularity of these particles lays in their low costs of production on one hand, and their good performance and stability on the other.
Typical plastic microbeads are smaller than 5 mm in diameter and are usually made form polyethylene (PE), polypropylene (PP), polymethylmethacrylate (PMMA), and in some cases, polyesters and polyamides. Unfortunately, the small size of PMs makes it hard for any water treatment plant to extract them from the water streams. Moreover, the high stability of these inert particles turns them into a big environmental problem, as they are spreading over the water bodies around the world and they have no hurry to degrade and disappear. To make the problem even worse, the plastic in these beads has high affinity for many toxic chemicals present in wastewaters. These chemicals are absorbed and adsorbed by the microparticles, which serve as vehicles to these poisonous chemicals that end up dispersed in the ocean. One of the most recent alarming findings is the presence of these poison-loaded microparticles in many animal species around the world.
A joined effort of different organizations and lawmakers gave birth to the Microbead-Free Waters act of 2015, an initiative that was turned into a national law on December of that year, when President Obama signed the bill. The new legislation mandates to phase out the manufacture of personal care products containing PMs by July 2017, and the sale of such cosmetic products by 2018, in the 50 states of the country. Other countries such as Canada, Australia, Germany and the UK are creating consciousness and following this example.
These changes in the statutory framework are compelling any company that sells PMs containing products to look for viable alternatives to the outlawed scrubbing particles. The webpage bitthemicrobread.org reports a list of 63 personal care product manufacturers that have publicly pledged to replace PMs in their products on or before 2017.
The transition, however, is not going to be easy, as it requires doing changes in the formulation, supplier chains, cost structure, etc. In fact, some companies represented by the Personal Care Products Council (PCPC), are trying to find loopholes in the new legislature, by tweaking the definition of “plastic microbeads”. This would allow these companies to replace the traditional PE or PP beads by other pernicious polylmeric materials. As it looks, some of the alternatives that these “rebellious” companies are considering are compostable plastic (CPs) such as cellulose acetate (the same present in cigarette butts) or polydroxyalcanoates (used in compostable cups and food containers). Although CPs can be degraded by microorganisms, high temperatures, acidic or alkaline conditions, or a combination of them; these materials are not better than the petrochemical microbeads, as they would not biodegrade in the marine environmental and they will still be strange bodies floating in our waters for, at least, tens of years.
As more people are becoming conscious of the impact that our everyday activities have on the environment and ecosystems, they are changing their habits in a positive way; users are becoming educated about the products they are buying, and the demand for environmentally friendly products is increasing. The cosmetic industry is a good example of this; the organic cosmetics' market is expected to grow at a compound annual growth rate of 9.6% from 2014 to 2020, when the global market is expected to reach $15.98 Billion. The industry for greener cosmetics blooms, as people are willing to pay more for products they can relate to as safer or healthier.
Although some brands have been offering natural alternatives to PMs for a while now, there does not seem to be an overtaking of the market by these solutions. Ground nutshells, pumice and natural waxes are among the frequently found raw exfoliating materials, but rice, coffee and almond grounds can be also found in some facial scrubs. The main limitation of these raw materials is that the functionality of the particles is restricted to the size of the grain, and there is little room for modification and optimization. For example, a facial scrub where the exfoliating agent is too harsh (pumice is a good example of this) is recommended for use at a lower frequency that the equivalent product formulated with PMs.
Limitations like this one represent an inconvenient both for the end user who does not want to use a potentially hurtful product, and the cosmetic manufacturer, who will try to avoid a drop in the sales of the product. The legal panorama leaves only two options to the cosmetic industry: to use the one of these natural, but off-putting, alternatives, or innovate and design new materials to revolutionize the field.
A different kind of solution is compulsory: an alternative as bio-friendly as the currently available raw scrubbing materials, but with the ability to adjust its properties according to the needs of the final product. The reader will agree that best alternative should, at the very least, feel and look as the traditional PMs do. To achieve this, it is essential to have a processable material that can be formulated, shaped and sized as desired with high reproducibility. The new alternative also needs to be 100% environmentally friendly to comply with the new legal framework.
The best solution to this problem needs to come from nature itself, yet in a way where the quality and properties of the final product can be controlled. Ideally, the solution will be to use macromolecules from plant origin as building blocks to create the new microparticles. By using 100% natural and FDA approved materials, biocompatibility of the microparticles is ensured.
Alginate-based hydrogel particles and beads have being around for years and different patents and publications present them as devices for cell encapsulation, drug delivery, cosmetic applications, food technology, etc. These hydrogels comprising alginate and other anionic polysaccharides are formed by electrostatic interactions between the biomolecule and an oppositely charged element (ionotropic gelation), usually a multivalent metal, in most cases is calcium. The resulting material is mechanically stable, has high affinity for water, is biocompatible, and biodegradable.
There is, however, a big limitation of these materials; and it is related to the hydrolytic stability of the gels. The nature of the interaction between the components of the gel makes it susceptible to degradation if the pH, ionic strength, temperature, or chemical composition of the environment change beyond certain levels. The outcome is a change in the gel volume, mechanical properties, and often dissolution of the material. This instability makes it difficult to use these gels for cosmetic applications, where complex mixtures of different chemicals are present, and the stability and shelf life of the final product is very important. One of the most common ingredients in soaps and shampoos, for instance, is EDTA. EDTA is used to chelate metal ions and improve the stability of the formulations. If a calcium-alginate hydrogel is added to a product containing this substance, the outcome would be the sequestration of the calcium by the EDTA and the complete disintegration of the hydrogel particle.
Different strategies for improving the hydrolytic stability of these polysaccharide gels include using mixtures of polysaccharides during the preparation of the gels, binding the particle in a layer to layer approach, or using other charged polymers for creating coatings on the surface of the hydrogel bead. None of these approaches yields a stable material that can endure the action of EDTA without undergoing degradation.
The method described herein combines the preparation of hydrogel particles, drying of the particles, and a solid-state reaction that results in the stabilization of the material and results in a microparticle with the following attributes:                Natural ingredients: Natural plant extracts are used to formulate materials.        Bio-friendly process: Process is 100% petrochemicals free and water is the only solvent used        Stability: Hydrolytic stability was tested in hand soap and in 2% EDTA solution. Beads are stable after 1 month, 40° C.        Color: Particles present a clear color that can be modified if desired.        Odor: Unlike some natural alternatives (coffee grounds, almonds, coconut, etc.) particles are odor free        Degradability: Being made from natural, plant-derived materials, the microparticles made in accordance with the embodiments of the invention are susceptible to enzymatic and hydrolytic degradation.        Size: Process allows for controlling the size of the particles with access to the micron and millimeter scales        Textures: Unlike some raw materials, microparticles produced in accordance with the embodiments of the invention do not present sharp edges that may cause laceration of the skin.        